Posterior Cruciate Ligament.

Improved understanding of the anatomy and biomechanics of the posterior cruciate ligament (PCL) has led to the evolution and improvement of anatomic-based reconstructions. The PCL is composed of the larger anterolateral bundle (ALB) and the smaller posteromedial bundle (PMB). On the femoral side, the ALB spans from the trochlear point to the medial arch point on the roof of the notch, while the PMB occupies the medial wall from the medial arch point to the most posterior aspect of the articular cartilage. Because of these broad and distinct attachments, the bundles have a load-sharing, synergistic and codominant relationship. Both restrict posterior translation; however, the ALB has a proportionally larger role in restricting translation throughout flexion, whereas the PMB has a role comparable to that of the ALB in full extension. In addition, the PMB resists internal rotational at greater flexion angles (> 90°). Consequently, it is difficult to restore native kinematics with a single graft. Biomechanical analysis of single- versus double-bundle PCL reconstructions (SB PCLR vs DB PCLR) demonstrates improved restoration of native kinematics with a DB PCLR, including resistance to posterior translation throughout flexion (15°-120°) and internal rotation in deeper flexion (90°-120°). Similarly, clinical research demonstrates excellent outcomes following DB PCLR, including functional outcomes comparable to those of anterior cruciate ligament reconstructions, with no significant differences between isolated and multiligament PCL injuries. Compared to SB PCLR, systematic review has demonstrated the superiority of DB PCLR based on objective postoperative stress radiography and International Knee Documentation Committee scores in randomized trials. In addition to reconstruction techniques, recent research has identified other factors that impact kinematics and PCL forces, including decreased tibial slope, which leads to increased graft stresses, and incidence of native PCL injuries. As the understanding of these other contributing factors evolves, so will surgical and treatment algorithms that will further improve patients' outcomes.

Intraoperative posterior movement of the tibia at 90° of flexion predicts worse postoperative flexion angles in cruciate-substituting total knee arthroplasty.

PURPOSE: To investigate the correlation between intraoperative tibiofemoral anteroposterior changes at 90° of flexion and postoperative maximum flexion angles in navigated cruciate-substituting TKA. The hypothesis of this study was that intraoperative tibiofemoral anteroposterior changes at 90° of flexion indirectly reflect posterior cruciate ligament (PCL) function and associate with postoperative maximum flexion angles. METHODS: Fifty-five consecutive patients with varus osteoarthritis treated with primary TKA were retrospectively analysed. All patients received the same type of implant, placed with an image-free navigation system. The PCL was retained, and cruciate-substituting inserts were used in all cases. The mean follow-up was 44 ± 8 months. The preoperative and postoperative kinematics were measured intraoperatively with a navigation system, and the preoperative and postoperative tibiofemoral anteroposterior positions at 90° of flexion were determined. The correlation between intraoperative anteroposterior position changes and postoperative maximum flexion angles was investigated. The correlation between the change of anteroposterior position and tibiofemoral rotational angles was also assessed. RESULTS: The intraoperative anteroposterior position change was -1.7 ± 3.4 mm (a positive value indicates tibial posterior shift). Flexion angle improvement was negatively correlated with intraoperative change of tibiofemoral anteroposterior position (R2 = 0.17, p < 0.005). Postoperative maximum flexion angles were also negatively correlated with intraoperative change of tibiofemoral anteroposterior position (R2 = 0.09, p < 0.05). The postoperative amount of tibial internal rotation was positively correlated with the preoperative amount (R2 = 0.60, p < 0.0001); however, the intraoperative anteroposterior position change was not correlated with the postoperative amount of tibial internal rotation (n.s.). CONCLUSION: A navigation system may be able to indirectly evaluate PCL function and predict the postoperative flexion angles in cruciate-substituting TKA. Intraoperative posterior movement of the tibia at 90° of flexion predicts worse postoperative flexion angles in cruciate-substituting TKA. LEVEL OF EVIDENCE: Level 3, retrospective comparative study.

Graft bending angle of the reconstructed posterior cruciate ligament gradually decreases as knee flexion increases.

PURPOSE: The purpose of the study was to determine the change in the graft bending angles at the femoral and tibial tunnel aperture in single-bundle posterior cruciate ligament (PCL) reconstruction. It was hypothesized that different knee flexion and different tunnel directions may affect changes of the femoral and tibial graft bending angle. METHODS: The right knees of 12 male subjects were scanned with a high-resolution computed tomography scanner at 4 different knee flexion angles (0°, 45°, 90° and 135°). To begin with, the 3D knee models were created and manipulated with the use of several modeling programs. Single-bundle PCL reconstruction was then virtually conducted in a 90° flexion model: The femoral and tibial graft bending angle, according to the various knee flexion angles, was calculated using a special software program. RESULTS: The femoral graft bending angle significantly decreased as the knee flexion increased between 0° and 135° (all p < 0.001). The femoral graft bending angle of the AL graft showed the most obtuse angles among the three types of the graft beyond 45° of knee flexion. For the tibial graft bending angle, the anteromedial tunnel group showed significantly more acute tibial graft bending angle than the anterolateral tunnel group in all three types of the graft at all flexion angles (all p < 0.001). CONCLUSION: Changes in the femoral graft bending angle were generally affected by different knee flexion angles. The effect of tibial tunnel direction on the tibial graft bending angle was found to be significant. The clinical relevance is that a mostly obtuse femoral graft bending angle was shown by the AL graft among three types of the graft.

In vivo kinematics and ligamentous function of the knee during weight-bearing flexion: an investigation on mid-range flexion of the knee.

PURPOSE: To investigate the in vivo femoral condyle motion and synergistic function of the ACL/PCL along the weight-bearing knee flexion. METHODS: Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging technique during a single-legged lunge (0°-120°). The medial and lateral femoral condyle translation and rotation (measured using geometric center axis-GCA), and the length changes of the ACL/PCL were analyzed at: low (0°-30°), mid-range (30°-90°) and high (90°-120°) flexion of the knee. RESULTS: At low flexion (0°-30°), the strains of the ACL and the posterior-medial bundle of the PCL decreased. The medial condyle showed anterior translation and lateral condyle posterior translation, accompanied with a sharp increase in external GCA rotation (internal tibial rotation). As the knee continued flexion in mid-range (30°-90°), both ACL and PCL were slack (with negative strain values). The medial condyle moved anteriorly before 60° of flexion and then posteriorly, accompanied with a slow increase of GCA rotation. As the knee flexed in high flexion (90°-120°), only the PCL had increasingly strains. Both medial and lateral condyles moved posteriorly with a rather constant GCA rotation. CONCLUSIONS: The ACL and PCL were shown to play a reciprocal and synergistic role during knee flexion. Mid-range reciprocal anterior-posterior femoral translation or laxity corresponds to minimal constraints of the ACL and PCL, and may represent a natural motion character of normal knees. The data could be used as a valuable reference when managing the mid-range "instability" and enhancing high flexion capability of the knee after TKAs. LEVEL OF EVIDENCE: Level IV.

Computational analysis of customized cruciate retaining total knee arthroplasty restoration of native knee joint biomechanics.

The purpose of this study was to verify if customized prosthesis better preserves the native knee joint kinematics and provides lower contact stress on the polyethylene (PE) insert owing to the wider bone preservation than that of standard off-the-shelf prosthesis in posterior cruciate-retaining type total knee arthroplasty (TKA). Validated finite element (FE) models for were developed to evaluate the knee joint kinematics and contact stress on the PE insert after TKA with customized and standard off-the-shelf (OTS) prostheses as well as in normal healthy knee through FE analysis under dynamic loading conditions. The contact stresses on the customized prosthesis decreased by 18% and 8% under gait cycle loading conditions, and 24% and 9% under deep-knee-bend loading conditions, in the medial and lateral sides of the PE insert, respectively, compared with the standard OTS prosthesis. The anterior-posterior translation and internal-external (IE) rotation in customized TKA were more similar to native knee joint behaviors compared with standard OTS TKA under gait loading conditions. The difference from normal knee kinematics was lower for femoral rollback and IE rotation in customized TKA than in standard OTS TKA in the deep-knee-bend condition. In general, customized prostheses achieve kinematics that are close to those of the native healthy knee joint and have better contact stresses than standard OTS prostheses in gait and deep-knee-bend loading conditions.

Elongation Patterns of the Anterior and Posterior Borders of the Anterolateral Ligament of the Knee.

PURPOSE: To compare the elongation patterns of the anterior and posterior borders of the anterolateral ligament (ALL) at varying knee flexion angles with the knee in a neutral position without any external forces and with external forces applied, including anterior-posterior translation, internal-external rotation, and varus-valgus angulation. METHODS: Eight cadaveric knees were tested in a custom knee testing system. Elongation of the anterior and posterior borders of the ALL was measured using a MicroScribe 3DLX system at knee flexion angles of 0°, 30°, 60°, and 90° and after the application of internal-external rotation, anterior-posterior translation, and varus-valgus angulation. RESULTS: The anterior border showed a slight noncontinuous increase in percentage elongation (0.8% ± 2.2%) whereas the posterior border showed a continuous decrease in percentage elongation (-12.0% ± 2.8%) as knee flexion increased (P < .001). Apart from the elongation of the posterior border at 90° of knee flexion, internal rotation, varus angulation, and anterior translation resulted in a significant increase in the percentage elongation of the anterior and posterior borders at each flexion angle compared with external rotation, valgus angulation, and posterior translation, respectively. CONCLUSIONS: The ALL shows different elongation patterns between the anterior and posterior borders, with a continuous decrease in the percentage elongation of the posterior border as knee flexion increases. CLINICAL RELEVANCE: This study presents useful evidence to resolve the uncertainty regarding the change in length of the ALL at various degrees of knee flexion. This information may be helpful for deciding the optimal knee flexion angle during ALL graft fixation. The findings from this study suggest that graft fixation during ALL reconstructions should be performed at close to full extension of the knee.

In vivo anterior cruciate ligament length pattern assessment secondary to differences in the femoral attachment under loading condition using image-matching techniques.

BACKGROUND: The anterior cruciate ligament is composed of two functional bundles and is crucial for knee function. There is limited understanding of the role of each individual bundle and the influence on length pattern due to difference in bone tunnel position under loading conditions throughout the range of motion. We measured point to point length between the femoral and tibial footprints of the ligament throughout the range of motion in normal knees, under normal loading conditions, and investigated length pattern changes secondary to differences in the femoral footprint. We hypothesized that anteromedial and posterolateral bundles have complementary roles, and the ligament length pattern is influenced by the footprint position. METHODS: We studied the squat movements of six healthy knees and measured point to point footprint distance. The footprint distances were measured after changing them to be 10% lower, 10% shallower, and both 10% lower and shallower than the defined anatomical femoral footprint. RESULTS: Average length changes of 12.0 and 14.1 mm from maximum extension (10°) to deep flexion (150°) were observed when the anteromedial and posterolateral bundles were defined by the default anatomical position. Maximum and minimum length were reached during full extension and flexion for both the anteromedial and posterolateral bundles, respectively. At 10% lower, length increased 2.2 mm over the default value in both the anteromedial and posterolateral lengths. At 10% shallower, decreases of 4.1 mm and 3.9 mm were observed compared with the default anteromedial and posterolateral lengths, respectively. In the 10% lower and 10% shallower position, anteromedial and posterolateral lengths decreased 2.1 mm and 1.9 mm compared with the default value, respectively. CONCLUSIONS: The anteromedial and posterolateral bundles have a complementary role. Femoral footprint position defined in the lower direction leads to stronger tension during extension, while the higher and shallower direction leads to isometry during flexion, and the deeper direction leads to laxity during flexion. The target bone tunnel position is that the anteromedial bundle should not to be too low and too deep to maintain function of bundle with less change in length. In addition, the posterolateral bundle should be somewhat lower and/or deeper than the anteromedial, with the expectation that it will function to induce stronger tension at the extended position. However, we should avoid lower position when we cannot prepare a sufficient diameter of reconstructed bundle to avoid re-injury due to excessive tension.

A Computer Model of Mid-Flexion Instability in a Balanced Total Knee Arthroplasty.

BACKGROUND: Some patients have mid-flexion instability despite stability at 0° and 90° of flexion. This study aims to determine the effects of total knee arthroplasty (TKA) stability while changing femur implant size and position. METHODS: A computational analysis was performed simulating knee flexion of posterior stabilized (PS) and cruciate retaining (CR) TKA designs. Deviations from the ideal TKA implant position were simulated by adjusting tibiofemoral proximal-distal position and femur anterior-posterior position as well as implant size. Forces in ligaments connecting the femur and tibia were collected. Total tibiofemoral ligament load for mid-knee flexion of 15°-75° was analyzed vs proximal-distal implant position, implant size, implant design, and knee flexion for PS and CR knees. Posterior cruciate ligament load was also analyzed for CR knees. RESULTS: Total tibiofemoral ligament load was significantly reduced by a more proximal tibiofemoral and anterior femur position (P < .001). Implant size did not have a significant effect on tibiofemoral ligament load (P > .1). Implant design and knee flexion significantly influenced total tibiofemoral ligament load (P < .001), but the interactions with implant proximal-distal position were not significant (P > .2), indicating that implant proximal-distal position had a similar effect across the 15°-75° knee flexion range for both studied PS and CR implant designs. CONCLUSION: PS and CR TKA can be well-balanced at 0° and 90° knee flexion and have instability in mid-flexion. Elevating the joint line and shifting the femur anteriorly can cause the knee to be too loose in mid-flexion.

[Choice of total knee arthroplasty: posterior cruciate ligament preserved or not].

Total knee arthroplasty is an effective method for the treatment of end-stage knee osteoarthrosis, which can effectively relieve joint pain and reconstruct the integrity of the joint. Whether the posterior cruciate ligament should be preserved during surgery or not, which is still in dispute. In recent years, posterior cruciate-retaining and substituting total knee prostheses are both applied in clinical practice. Both domestic and international studies have shown that there are no significant difference in patient satisfaction, knee flexion, survival rate of the prosthesis and the main clinical manifestations between two prostheses. However, posterior cruciate-retaining total knee prosthesis is more consistent with the normal physiology and biomechanics of the human body. The gait is more balanced and proprioceptive when walking up and down the stairs, but when the joints are buckling, the femur is abnormal to move back to the tibia, resulting in abnormal motion. While posterior cruciate-substituting total knee prosthesis can correct severe deformity of the knee, and keep better balance between flexion and extension of the knee joint, but there is a potential complication of patellar clunk syndrome. Therefore, under the same conditions, the younger patients may prefer to chose posterior cruciate-retaining total knee prosthesis, while elder patients may prefer to chose posterior cruciate-substituting total knee prosthesis. This paper reviews the function of posterior cruciate ligament, as well as the advantages and disadvantages of two prostheses, so as to provide some references for clinic.

Rupture of posterior cruciate ligament leads to radial displacement of the medial meniscus.

BACKGROUND: To explore the association between the rupture of posterior cruciate ligament (PCL) and the radial displacement of medial meniscus under the conditions of different flexion and various axial loads. METHODS: The radial displacement value of medial meniscus was measured for the specimens of normal adult knee joints, including 12 intact PCLs, 6 ruptures of the anterolateral bundle (ALB), 6 ruptures of the postmedial bundle (PMB), and 12 complete ruptures. The measurement was conducted at 0°, 30°, 60°, and 90° of knee flexion angles under 200 N, 400 N, 600 N, 800 N and 1000 N of axial loads respectively. RESULTS: The displacement values of medial meniscus of the ALB rupture group increased at 0° flexion under 800 N and 1000 N, and at 30°, 60° and 90° flexion under all loads in comparison with the PCL intact group. The displacement values of the PMB rupture group was higher at 0° and 90° flexion under all loads, and at 30° and 60° flexion under 800 N and 1000 N loads. The displacement of the PCL complete rupture group increased at all flexion angles under all loads. CONCLUSIONS: Either partial or complete rupture of the PCL can increase in the radial displacement of the medial meniscus, which may explain the degenerative changes that occuring in the medial meniscus due to PCL injury. Therefore, early reestablishment of the PCL is necessarily required in order to maintain stability of the knee joint after PCL injury.

Kinematics of Different Components of the Posterolateral Corner of the Knee in the Lateral Collateral Ligament-intact State: A Human Cadaveric Study.

PURPOSE: To determine the static stabilizing effects of different anatomical structures of the posterolateral corner (PLC) of the knee in the lateral collateral ligament (LCL)-intact state. METHODS: Thirteen fresh-frozen human cadaveric knees were dissected and tested using an industrial robot with an optical tracking system. Kinematics were determined for 134 N anterior/posterior loads, 10 N m valgus/varus loads, and 5 N m internal/external rotatory loads in 0°, 20°, 30°, 60°, and 90° of knee flexion. The PLC structures were dissected and consecutively released: (I) intact knee joint, (II) with released posterior cruciate ligament (PCL), (III) popliteomeniscal fibers, (IV) popliteofibular ligament, (V) arcuat and popliteotibial fibers, (VI) popliteus tendon (PLT), and (VII) LCL. Repeated-measures analysis of variance was performed with significance set at P < .05. RESULTS: After releasing the PCL, posterior tibial translation increased by 5.2 mm at 20° to 9.4 mm at 90° of joint flexion (P < .0001). A mild 1.8° varus instability was measured in 0° of flexion (P = .0017). After releasing the PLC structures, posterior tibial translation further increased by 2.9 mm at 20° to 5.9 mm at 90° of flexion (P < .05) and external rotation angle increased by 2.6° at 0° to 7.9° at 90° of flexion (P < .05, vs II). Varus stability did not decrease. Mild differences between states V and VI were found in 60° and 90° external rotation tests (2.1° and 3.1°; P < .05). CONCLUSIONS: The connecting ligaments/fibers to the PLT act as a primary static stabilizer against external rotatory loads and a secondary stabilizer against posterior tibial loads (when PCL is injured). After releasing these structures, most static stabilizing function of the intact PLT is lost. The PLC has no varus-stabilizing function in the LCL-intact knee. CLINICAL RELEVANCE: Anatomy and function of these structures for primary and secondary joint stability should be considered for clinical diagnostics and when performing surgery in the PLC.

In vivo posterior cruciate ligament elongation in running activity after anatomic and non-anatomic anterior cruciate ligament reconstruction.

PURPOSE: The goals of this study were to (1) investigate the in vivo elongation behaviour of the posterior cruciate ligament (PCL) during running in the uninjured knee and (2) evaluate changes in PCL elongation during running after anatomic or non-anatomic anterior cruciate ligament (ACL) reconstruction. METHODS: Seventeen unilateral ACL-injured subjects were recruited after undergoing anatomic (n = 9) or non-anatomic (n = 8) ACL reconstruction. Bilateral high-resolution CT scans were obtained to produce 3D models. Anterolateral (AL) and posteromedial (PM) bundles insertion sites of the PCL were identified on the 3D CT scan reconstructions. Dynamic knee function was assessed during running using a dynamic stereo X-ray (DSX) system. The lengths of the AL and PM bundles were estimated from late swing through mid-stance. The contralateral knees served as normal controls. RESULTS: Control knees demonstrated a slight decrease in AL bundle and a significant decrease in PM bundle length following foot strike. Length and elongation patterns of the both bundles of the PCL in the anatomic ACL reconstruction group were similar to the controls. However, the change in dynamic PCL length was significantly greater in the non-anatomic group than in the anatomic reconstruction group after foot strike (p < 0.05). CONCLUSION: The AL bundle length decreased slightly, and the PM bundle length significantly decreased after foot strike during running in uninjured knees. Anatomic ACL reconstruction maintained normal PCL elongation patterns more effectively than non-anatomic ACL reconstruction during high-demand, functional loading. These results support the use of anatomic ACL reconstruction to achieve normal knee function in high-demand activities. LEVEL OF EVIDENCE: Case-control study, Level III.

Effect of Posterior Cruciate Ligament Rupture on Biomechanical and Histological Features of Lateral Femoral Condyle.

BACKGROUND The aim of this study was to investigate bone mineral density (BMD) and the biomechanical and histological effects of posterior cruciate ligament (PCL) rupture on the lateral femoral condyle. MATERIAL AND METHODS Strain on different parts of the lateral femoral condyle from specimens of normal adult knee joints, including 12 intact PCLs, 6 ruptures of the anterolateral bundle, 6 ruptures of the postmedial bundle, and 12 complete ruptures, was tested when loaded with different loads on the knee at various flexion angles. Lateral femoral condyles were also collected randomly from both the experimental side in which the PCLs were transected and the control side from 4 sets of 12 matched-mode pairs of rabbits at 4, 8, 16, and 24 weeks after surgery, and their BMD and morphological and histological changes were observed. RESULTS Partial and complete rupture of the PCL may cause an abnormal load on all parts of the lateral femoral condyle with any axial loading at all positions. Noticeable time-dependent degenerative histological changes of the lateral femoral condyle were observed in the rabbit model of PCL rupture. All of the PCL rupture groups had a higher expression of matrix metalloproteinase-7 (MMP-7) and collagen type II than the control group at all time points (P<0.05), but no significant difference in BMD (P>0.05). CONCLUSIONS Rupture of the PCL may trigger a coordinated response of lateral femoral condyle degeneration in a time-dependent manner, to which the high level of expression of MMP-7 and collagen type II could contribute.

Postoperative Knee Flexion Angle Is Affected by Lateral Laxity in Cruciate-Retaining Total Knee Arthroplasty.

BACKGROUND: Although many studies have reported that postoperative knee flexion is influenced by preoperative conditions, the factors which affect postoperative knee flexion have not been fully elucidated. We tried to investigate the influence of intraoperative soft tissue balance on postoperative knee flexion angle after cruciate-retaining (CR) total knee arthroplasty (TKA) using a navigation and an offset-type tensor. METHODS: We retrospectively analyzed 55 patients with osteoarthritis who underwent TKA using e.motion-CR (B. Braun Aesculap, Germany) whose knee flexion angle could be measured at 2 years after operation. The exclusion criteria included valgus deformity, severe bony defect, infection, and bilateral TKA. Intraoperative varus ligament balance and joint component gap were measured with the navigation (Orthopilot 4.2; B. Braun Aesculap) while applying 40-lb joint distraction force at 0° to 120° of knee flexion using an offset-type tensor. Correlations between the soft tissue parameters and postoperative knee flexion angle were analyzed using simple linear regression models. RESULTS: Varus ligament balance at 90° of flexion (R = 0.56; P < .001) and lateral compartment gap at 90° of flexion (R = 0.51; P < .001) were positively correlated with postoperative knee flexion angle. In addition, as with past studies, joint component gap at 90° of flexion (R = 0.30; P < .05) and preoperative knee flexion angle (R = 0.63; P < .001) were correlated with postoperative knee flexion angle. CONCLUSION: Lateral laxity as well as joint component gap at 90° of flexion is one of the most important factors affecting postoperative knee flexion angle in CR-TKA.

An Intact Anterior Cruciate Ligament at the Time of Posterior Cruciate Ligament-Retaining Total Knee Arthroplasty Was Associated With Reduced Patient Satisfaction and Inferior Pain and Stair Function.

BACKGROUND: Patients with an intact anterior cruciate ligament (ACL) at the time of ACL-sacrificing total knee arthroplasty (TKA) have been suggested to have inferior outcomes compared with those with a dysfunctional ACL. However, to date, no published clinical studies have evaluated the potential link between the condition of the ACL at the time of posterior cruciate ligament-retaining TKA and postoperative pain, function, and satisfaction. As such, the purpose of this study was to compare subjective function, movement-elicited pain, pain at rest, and patient satisfaction between those with an intact or dysfunctional ACL. METHODS: We identified 562 posterior cruciate ligament-retaining TKAs with complete intraoperative and postoperative data. Patients were categorized based on the condition of the ACL at the time of TKA as either being intact or dysfunctional (absent or lax). Knee Society Function Scores, movement-elicited pain, pain at rest, and patient satisfaction were then compared between groups. RESULTS: At mean follow-up of 5.1 years, a significantly lower proportion of patients in the intact group were satisfied with their operation (intact: 391/453 [86.3%] vs dysfunctional: 102/109 [93.6%], P = .0496). Inspection of the individual activities revealed that the groups did not differ in walking ability or pain when walking; however, the intact group reported significantly reduced ability to navigate stairs with greater pain during that activity. CONCLUSION: The lack of difference in pain at rest between groups suggests that pain and functional impairments during more demanding activities such as navigating stairs may be associated with the lost function of the ACL rather than by altered central pain processing.

Complex function of the knee joint: the current understanding of the knee.

Since the early years of orthopaedics, it is a well-known fact that anatomy follows function. During the evolution of mankind, the knee has been optimally adapted to the forces and loads acting at and through the knee joint. However, anatomy of the knee joint is variable and the only constant is its complex function. In contrast to the time of open surgery, nowadays the majority of reconstructive knee surgery is done arthroscopically. Keyhole surgery is less invasive, but on the backside, the knee surgeon lacks daily visualisation of the complex open anatomy. As open anatomical knowledge is less present in our daily practice, it is even more important to highlight this complex anatomy and function of the knee. It is the purpose of this review to perform a systematic review of knee anatomy, highlight the complex function of the knee joint and present an overview about recent and current knowledge about knee function. Level of evidence Systematic review, Level IV.

Is the posterior cruciate ligament necessary for medial pivot knee prostheses with regard to postoperative kinematics?

PURPOSE: Excellent clinical and kinematical performance is commonly reported after medial pivot knee arthroplasty. However, there is conflicting evidence as to whether the posterior cruciate ligament should be retained. This study simulated how the posterior cruciate ligament, post-cam mechanism and medial tibial insert morphology may affect postoperative kinematics. METHODS: After the computational intact knee model was validated according to the motion of a normal knee, four TKA models were built based on a medial pivot prosthesis; PS type, modified PS type, CR type with PCL retained and CR type with PCL sacrificed. Anteroposterior translation and axial rotation of femoral condyles on the tibia during 0°-135° knee flexion were analyzed. RESULTS: There was no significant difference in kinematics between the intact knee model and reported data for a normal knee. In all TKA models, normal motion was almost fully restored, except for the CR type with PCL sacrificed. Sacrificing the PCL produced paradoxical anterior femoral translation and tibial external rotation during full flexion. CONCLUSION: Either the posterior cruciate ligament or post-cam mechanism is necessary for medial pivot prostheses to regain normal kinematics after total knee arthroplasty. The morphology of medial tibial insert was also shown to produce a small but noticeable effect on knee kinematics. LEVEL OF EVIDENCE: V.

Control of paradoxical kinematics in posterior cruciate-retaining total knee arthroplasty by increasing posterior femoral offset.

PURPOSE: Balancing the posterior cruciate ligament (PCL) with posterior cruciate-retaining total knee replacement (PCR-TKR) aims to restore femoral rollback. In practice, paradoxical roll forward persists. The purpose of this study is to propose a technique for optimizing PCL tension. Because PCL function starts above 60° of flexion, we hypothesize that PCL balancing requires flexion gap tightening by oversizing the femoral component and increasing posterior condylar offset (PCO). METHODS: PCR-TKR was performed in 21 osteoarthritis patients with a gap-balancing technique. The femoral component was oversized if more than a 5-mm posterior drawer existed after tibial component implantation. Kinematics was recorded intra-operatively in two steps with dedicated navigation software (Praxim, La Tronche, Isère, France): antero-posterior (AP) displacements of condylo-tibial contact points were observed in native and implanted knees, with each knee serving as its own control. The absence of paradoxical displacements was verified once the final implants were inserted. RESULTS: Paradoxical medial condyle displacement (11 mm) persisted in a single case. On average, posterior displacement of the medial condyle decreased from 9 ± 9 to 1 ± 6 mm (p = 0.001) and that of the lateral condyle from 16 ± 14 to 6 ± 6 mm (p = 0.006). In the 0°-30° flexion interval, posterior displacement was 2 times less than before implantation for the medial condyle (p = 0.001), and 4 times less for the lateral condyle (p = 0.004). The course of the lateral condyle decreased from 2 ± 3 to 0 ± 4 mm in the 90°-120° flexion interval (p = 0.046). Six-month flexion was 124° ± 17°. CONCLUSION: Femoral component oversizing allows us to control paradoxical forward displacements in 95 % of cases. When balancing PCR prostheses, AP laxity should be taken into account. Increasing PCO appears to be a reliable technique for adjusting PCL balance. Thus, it may optimize extensor mechanism action and, subsequently, the functional results of PCR-TKR. LEVEL OF EVIDENCE: Diagnostic study, Level II.

Regaining Native Knee Kinematics Following Joint Arthroplasty: A Novel Biomimetic Design with ACL and PCL Preservation.

Lack of ACL and non-anatomic articular surfaces in contemporary total knee implants result in kinematic abnormalities. We hypothesized that such abnormalities may be addressed with a biomimetic bi-cruciate retaining (BCR) design having anatomical articular surfaces. We used dynamic computer simulations to compare kinematics among the biomimetic BCR, a contemporary BCR and cruciate-retaining implant for activities of daily living. During simulated deep knee bend, chair-sit and walking, the biomimetic BCR implant showed activity dependent kinematics similar to healthy knees in vivo. Restoring native knee geometry together with ACL preservation provided these kinematic improvements over contemporary ACL-preserving and ACL-sacrificing implants. Further clinical studies are required to determine if such biomimetic implants can result in more normal feeling knees and improve quality of life for active patients.

Posterior cruciate ligament balancing in total knee arthroplasty: a numerical study with a dynamic force controlled knee model.

BACKGROUND: Adequate soft tissue balancing is a key factor for a successful result after total knee arthroplasty (TKA). Posterior cruciate ligament (PCL) is the primary restraint to posterior translation of the tibia after cruciate retaining TKA and is also responsible for the amount of joint compression. However, it is complex to quantify the amount of ligament release with its effects on load bearing and kinematics in TKA and limited both in vivo and in vitro. The goal of this study was to create a dynamic and deformable finite element model of a full leg and analyze a stepwise release of the PCL regarding knee kinematics, pressure distribution and ligament stresses. METHODS: A dynamic finite element model was developed in Ansys V14.0 based on boundary conditions of an existing knee rig. A cruciate retraining knee prosthesis was virtually implanted. Ligament and muscle structures were simulated with modified spring elements. Linear elastic materials were defined for femoral component, inlay and patella cartilage. A restart algorithm was developed and implemented into the finite element simulation to hold the ground reaction force constant by adapting quadriceps force. After simulating the unreleased PCL model, two models were developed and calculated with the same boundary conditions with a 50% and 75% release of the PCL stiffness. RESULTS: From the beginning of the simulation to approximately 35° of flexion, tibia moves posterior related to the femur and with higher flexion anteriorly. Anterior translation of the tibia ranged from 5.8 mm for unreleased PCL to 3.7 mm for 75% PCL release (4.9 mm 50% release).A decrease of maximum von Mises equivalent stress on the inlay was given with PCL release, especially in higher flexion angles from 11.1 MPa for unreleased PCL to 8.9 MPa for 50% release of the PCL and 7.8 MPa for 75% release. CONCLUSIONS: Our study showed that dynamic FEM is an effective method for simulation of PCL balancing in knee arthroplasty. A tight PCL led in silico to more anterior tibia translation, a higher collateral ligament and inlay stress, while retropatellar pressure remained unchanged. Surgeons may take these results in vivo into account.